Walnuts are the healthiest of all the nuts and should be eaten more as part of a healthy diet, US scientists say.
Scientists from Pennsylvania told the American Chemical Society that walnuts contain the highest level of antioxidants compared to other nuts.
Antioxidants are known to help protect the body against disease.
The scientists said that all nuts have good nutritional qualities but walnuts are healthier than peanuts, almonds, pecans and pistachios.
Dr Joe Vinson, from the University of Scranton, analysed the antioxidant levels of nine different types of nuts and discovered that a handful of walnuts contained twice as many antioxidants as a handful of any other commonly eaten nut.
He found that these antioxidants were higher in quality and potency than in any other nut.
Antioxidants are good because they stop the chain reactions that damage cells in the body when oxidation occurs.
The antioxidants found in walnuts were also two to 15 times as powerful as vitamin E, which is known to protect the body against damaging natural chemicals involved in causing disease, the study says.
Nuts are known to be healthy and nutritious, containing high-quality protein, lots of vitamins and minerals as well as dietary fibre. They are also dairy and gluten-free.
Previous research has shown that regular consumption of small amounts of nuts can reduce the risk of heart disease, some types of cancer, type two diabetes and other health problems.
Dr Vinson said there was another advantage in choosing walnuts as a source of antioxidants: "The heat from roasting nuts generally reduces the quality of the antioxidants.
"People usually eat walnuts raw or unroasted, and get the full effectiveness of those antioxidants."